Researchers recently assessed various AS-OCT scanning protocols for corneal thickness measures and found that AS-OCT volumetric scans over a central 6mm of the cornea provide highly repeatable measures of epithelial, stromal and total corneal thickness. The scan included three lines each consisting of 20 B-scans.
The study evaluated 15 adults using single 8.3mm-wide horizontal line scans with an average of two, 10, 20, 30, 50 and 100 B-scans. The team also used volumetric scans consisting of nine 8.3mm horizontal line scans encompassing a 1.3mm vertical region (with 20 B-scans per line scan). They compared single-point thickness measures with thickness measures averaged over the central 6mm and analyzed the impact of B-scan average and intra-observer variability for single line scans. For volumetric scans, they calculated the impact the number of line scans had on intra-observer and intra-session variability.
The investigators discovered that intra-observer repeatability did not vary significantly based on the number of average B-scans per line scan but was lowest for 20 to 30 averaged scans. For volumetric scans, they noted that increasing the number of line scans increased scan duration, with minimal impact on the average scan quality index. They added that averaging more than three line scans did not significantly improve intra-observer or intra-session repeatability for either single point or average thickness measurements.
“This scanning protocol can provide reliable information when monitoring subtle changes in corneal thickness,” the study authors concluded in their paper.
|Fisher D, Collins MJ, Vincent SJ. Anterior segment optical coherence tomography scanning protocols and corneal thickness repeatability. Contact Lens Anterior Eye. December 18, 2019. [Epub ahead of print].